Heat sink has been the traditional name for devices that transfer heat from a heat generator to lower-temperature surroundings with a design objective of minimizing the temperature rise between the heat generator and the surroundings. The purpose is to keep the temperature of the heat generator low to prevent performance degradation or destruction of the generator. Electronic equipment and components wherein a temperature of 50.degree. C. represents a benign environment, but 120.degree. C. represents complete destruction, use heat sinks in great abundance and variety.
The heat sinks of this invention not only transfer heat, they absorb heat. Obviously heat absorption can only exist in a transient situation and a major purpose of such heat sinks is to delay temperature rise until the equipment is no longer required to operate or until the temperature of the surroundings goes down.
Delay in temperature rise can be vitally important. Missiles and space vehicles are only subjected to intense heat for periods of several minutes and often their equipment is only required to operate for several minutes. There are a multitude of other examples wherein heat removal for a short time is a key design requirement.
Two heat-absorbing phenomina are used here. One occurs when using a melting compound in the heat sink. Any solid when melting absorbs heat without temperature rise. The quantity of heat absorbed to convert a unit solid mass to liquid mass at the same temperature is called the latent heat of fusion. The other phenomina occurs when using a compound in the heat sink that undergoes a chemical change at a specific temperature, absorbing heat. Such a reaction is called an endothermic reaction.
It is clear that a change of a solid to a liquid creates the problem of containing the liquid that was once a solid. Similar changes occur in endothermic reactions. Melting compounds have been sealed inside cavities in heat sinks so as not to escape in liquid form. This involves sealing problems including allowance for expansion with temperature, and does not improve heat transfer by covection and radiation as is accomplished by the invention here. The use of heat-absorbing compounds in heat sinks does not appear in any known patent.